An Efficient Diffusing - vortex Sheet Algorithm for Soving Unsteady Boundary Layer Equations

摘要

A new diffusing-vortex sheet algorithm for solving unsteady boundary layers is presented. The method is related to earlier random vortex and diffusing-vortex methods. The main features of this method are: (i) the velocity and vorticity field are represented by segments of a non-rotating vorticity sheet of negligible thickness, and (ii) the direct implementation of the diffusion process. To avoid the singularity associated with a vorticity sheet at the time of birth at the wall, an initial distribution according to the known asymptotic solution is used as a start. The advantage of this methods is evidenced by the fact that (i) the accurate instantaneous velocity profiles have been obtained; (ii) numerical computation is confined in a single reference station, thus significantly reducing CPU time. Several new instantaneous velocity profiles and wall shear stress are presented for a number of impulsively started wedge type flows.